"Signature" was a widely used term in medical literature up to the 17th century. The shape and colour of plants and their parts was believed to reveal their medical properties, as a "signature" prepared by Divine Providence in order to lead Man to his physical remedies. Heart-shaped leaves showed that the plant was good for heart diseases.
Finnegans Wake is studded with signatures, or stickers, tags, labels, pointers, more or less disguised references, which can lead the reader to quotes, passages, and books beyond Joyce’s own text. However, these extraneous texts sometimes appear to relate to each other, at least as neighbouring books on our shelves should, thus contributing their external impulses to the dynamics of the original text. This transtextual effect is far easier to observe in the Wake than in Ulysses but I hold that the same method can be detected in Ulysses with the help of sufficient Wake training. The following observation may serve as a typical example of signatures in Finnegans Wake (68/18ff).
In an Italian cluster, preceded by "sfidare" (‘defy’) and thrice "tease fido" = ti sfido (‘I defy you’) one line above, and followed by "Bissavolo" on the next line (meaning Great-Great-Grandfather', thus dating at least 4 generations back), the highlighted invocation "Angealousmei!" (68/18), Angel, Angelus mine, is obviously matched by "Tawfulsdreck!" (68/22: ‘Devilshit’), a similar invocation, invoking not only the enhanced contrary of an angel but also Professor Teufelsdröckh1 from Thomas Carlyle’s Sartor Resartus, a quite revolutionary and revolting satirical pamphlet of 1831.
The evident symmetry of the two signatures suggests an equally important literary background for "Angealousmei!", preferably revolutionary, age-matched, and at least as evocative to well-read readers. These conditions are met, not in English but in Italian literature, by Giacomo Leopardi`s revolutionary poem "Ad Angelo Mai" of 1820, written "When he had found Cicero`s books on the Republic".
Angelo Mai, 1782-1854, a Jesuit philologist, Librarian of the Ambrosiana (Milan) and the Vaticana, appointed Cardinal in 1837, discovered and edited a number of Greek and Latin manuscripts. Giacomo Leopardi, 1798-1897, was one of the precursors of the Italian revolution, the Risorgimento, and his poem `To Angelo Mai', hailed as the clarion call of the Risorgimento, evokes an ideal Italy as in Roman times, in stark contrast with the miserable political realities of his own time:
Leopardi attempted to publish his collected works in Naples in 1835, but the Bourbon Government suppressed the last two of the planned four volumes, and the pages that had been printed ended up as pulp. A similar disaster later struck Joyces Dubliners which were burned, as celebrated in his polemical poem "Gas from a Burner" (in turn inspired by a similar poem on a similar disaster by James Charles Lever, an earlier Dublin writer who also ended up in Trieste)
Conclusion: Joyce confronts his readers with signatures, indicating "thereby hangs a tale". These stickers or labels are marked by their prominent position in the text, and by further signals, in this example, exclamation points. Their function is identical with that of the signal for " appended document" in current computer programs: readers may open it if they obtain the key, that is, if they find out that Carlyle’s Sartor Resartus is indicated by “Tawfulsdreck”, and that Leopardis Ad Angelo Mai is indicated by “Angealousmei”. They will be rewarded with a discourse resulting from the parallel properties of both texts. But Joyce is not an easy author, and his Angelo Mai has been so carefully hidden that even the Italian translation missed it completely - despite the great popularity of Leopardi’s poems among senior literate Italians who still carry them about in their pockets in suitable miniature volumes (Le Poesie, Barbèra, Florence 1900)
1 Teufelsdröckh`s friend who provides the information for Sartor Resartus is "Herr Hofrath Heuschreck" (‘Grasshopper’): an precursor of The Ondt and the Gracehoper”?